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  • 1
    Online Resource
    Online Resource
    Syntactic Iron Foams’ Properties Tailored by Means of Case Hardening via Carburizing or Carbonitriding
    MDPI AG ; 2021
    In:  Materials Vol. 14, No. 16 ( 2021-08-04), p. 4358-
    Details
    In: Materials, MDPI AG, Vol. 14, No. 16 ( 2021-08-04), p. 4358-
    Abstract: Metal foam inserts are known for their high potential for weight and vibration reduction in composite gear wheels. However, most metal foams do not meet the strength requirements mandatory for the transfer of sufficiently high levels of torque by the gears. Syntactic iron and steel foams offer higher strength levels than conventional two-phase metal foams, thus making them optimum candidates for such inserts. The present study investigates to what extent surface hardening treatments commonly applied to gear wheels can improve the mechanical properties of iron-based syntactic foams. Experiments performed thus focus on case hardening treatments based on carburizing and carbonitriding, with subsequent quenching and tempering to achieve surface hardening effects. Production of samples relied on the powder metallurgical metal injection molding (MIM) process. Syntactic iron foams containing 10 wt.% of S60HS hollow glass microspheres were compared to reference materials without such filler. Following heat treatments, the samples’ microstructure was evaluated metallographically; mechanical properties were determined via hardness measurements on reference samples and 4-point bending tests, on both reference and syntactic foam materials. The data obtained show that case hardening can indeed improve the mechanical performance of syntactic iron foams by inducing the formation of a hardened surface layer. Moreover, the investigation indicates that the respective thermo-chemical treatments can be applied to composite gear wheels in exactly the same way as to monolithic ones. In the surface region modified by the treatment, martensitic microstructures were observed, and as consequence, the bending limits of syntactic foam samples were increased by a factor of three.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma14164358
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2487261-1
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  • 2
    Online Resource
    Online Resource
    Hydrogen Absorption during Case Hardening of Steels EN20MnCr5 (SAE5120) and EN18CrNiMo7-6 (SAE4820)
    MDPI AG ; 2021
    In:  Metals Vol. 12, No. 1 ( 2021-12-21), p. 6-
    Details
    In: Metals, MDPI AG, Vol. 12, No. 1 ( 2021-12-21), p. 6-
    Abstract: Damages to case-hardened components are often associated with the phenomenon of hydrogen embrittlement due to their specific fracture pattern. In the present work, the effects of the case hardening process on the hydrogen content in the material were investigated and the effects of hydrogen on the mechanical properties were examined. In order to determine not only the influence of the heat treatment process but also the influence of the material, the case-hardening steels EN20MnCr5 (SAE5120) and EN18CrNiMo7-6 (SAE4820) with different degrees of purity were investigated. From the results it can be deduced that the sulphidic and oxidic inclusions have no significant influence on the hydrogen content. When checking the mechanical properties, it was shown in the incremental step loading technique according to ASTM F1624 that a purely case-hardened condition only has a slight tendency to hydrogen embrittlement. However, if the material is additionally loaded with hydrogen, the material fails significantly below the maximum expected load in the incremental step loading test, which is to be interpreted as a clear indication of failure due to hydrogen embrittlement. However, the fracture patterns of these two states do not show any significant differences. Therefore, it does not seem possible to attribute damage to a case-hardened component to hydrogen embrittlement on the basis of the fracture pattern alone.
    Type of Medium: Online Resource
    ISSN: 2075-4701
    URL: Article
    DOI: 10.3390/met12010006
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2662252-X
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  • 3
    Online Resource
    Online Resource
    Investigation of combined surface treatments and coatings to increase the wear behavior of heat treatable steels
    Elsevier BV ; 2023
    In:  Surface and Coatings Technology Vol. 472 ( 2023-11), p. 129929-
    Details
    In: Surface and Coatings Technology, Elsevier BV, Vol. 472 ( 2023-11), p. 129929-
    Type of Medium: Online Resource
    ISSN: 0257-8972
    URL: Article
    DOI: 10.1016/j.surfcoat.2023.129929
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2023
    detail.hit.zdb_id: 1502240-7
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  • 4
    Online Resource
    Online Resource
    Carbonitriding of Forging Dies
    MDPI AG ; 2021
    In:  Metals Vol. 11, No. 10 ( 2021-10-18), p. 1651-
    Details
    In: Metals, MDPI AG, Vol. 11, No. 10 ( 2021-10-18), p. 1651-
    Abstract: Forging dies have to resist high mechanical and thermal loads. Therefore, they are usually nitrided. Former investigations showed that the abrasive wear at the critical parts of the dies is much higher than the nitriding hardness depth. Carbonitriding offers the possibility to increase the hardness depth in shorter treatment times because of the higher treatment temperature. The (carbo-)nitrided surface region obtains a better hardness at elevated temperatures and a better wear resistance than the untreated steel. In order to create a wear- and corrosion-resistant compound layer at the surface, a nitriding process step can be conducted after carbonitriding. The present work deals with developing a carbonitriding treatment for forging dies and investigations on the wear resistance of the created surface zones in model wear tests and tool life time experiments under industrial conditions. The aim of this work was to produce heat- and wear-resistant precipitation layers in hot working tool steels in economical treatment durations.
    Type of Medium: Online Resource
    ISSN: 2075-4701
    URL: Article
    DOI: 10.3390/met11101651
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
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  • 5
    Online Resource
    Online Resource
    Impact of pre-machining on the surface and subsurface characteristics of deep rolled metastable austenitic 18CrNiMo7-6
    Elsevier BV ; 2022
    In:  Procedia CIRP Vol. 108 ( 2022), p. 630-635
    Details
    In: Procedia CIRP, Elsevier BV, Vol. 108 ( 2022), p. 630-635
    Type of Medium: Online Resource
    ISSN: 2212-8271
    URL: Article
    DOI: 10.1016/j.procir.2022.03.099
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2022
    detail.hit.zdb_id: 2674706-6
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  • 6
    Online Resource
    Online Resource
    Systematische Untersuchung verschiedener Einflussgrößen auf die Maß- und Formänderungen von einsatzgehärteten Stirnrädern* : Teil 1: Grundkörperverzug
    Walter de Gruyter GmbH ; 2012
    In:  HTM Journal of Heat Treatment and Materials Vol. 67, No. 1 ( 2012-02-01), p. 65-78
    Details
    In: HTM Journal of Heat Treatment and Materials, Walter de Gruyter GmbH, Vol. 67, No. 1 ( 2012-02-01), p. 65-78
    Abstract: Hoch belastete Zahnräder werden üblicherweise wärmebehandelt, um den betriebsbedingten Belastungen zu widerstehen. Im Zusammenhang mit Bauteilen des Antriebstrangs, insbesondere Zahnrädern, wird häufig das Verfahren des Einsatzhärtens eingesetzt. Dabei werden verschiedene Verzüge beobachtet, deren Untersuchung im Folgenden dargestellt wird. Als Probekörper dienten schrägverzahnte kleinmodulige Stirnräder. Die Einsatzhärtung wurde in einer Zwei-Kammer-Vakuumanalage vom Typ IPSEN RVTC 224 mittels Niederdruckaufkohlen und Hochdruckgasabschreckung durchgeführt. Die Untersuchungen wurden durch die Anwendung von Design-of-Experiments (DoE)-Methoden unterstützend begleitet. Bezüglich ihres Einflusses auf den Verzug der Zahnräder standen die drei aufeinanderfolgenden Wärmebehandlungsschritte Erwärmen, Aufkohlen und Abschrecken im Fokus der Untersuchungen. Die in den Untersuchungen des Erwärmprozesses variierten Parameter sind der Chargenaufbau, der Wärmeübergangsmechanismus sowie die Temperatur der ersten Haltestufe für den Temperaturausgleich in der Charge. Die in der Aufkohlung variierten Größen sind die Aufkohlungstiefe und der Randkohlenstoffgehalt sowie die Atmosphäre während der Diffusions- und Haltephasen. Das Abschrecken wurde nicht variiert. Die Änderung der Maß- und Formabweichungen durch die Wärmebehandlung wurde durch 3-D-Koordinatenmessung des Grundkörpers und der Verzahnung vor und nach der Wärmebehandlung ermittelt. Die Einflüsse der untersuchten Parameter auf die Maß- und Formänderungen der Zahnräder wurden durch eine Varianzanalyse der Versuchsergebnisse statistisch bewertet und die Signifikanz verifiziert.
    Type of Medium: Online Resource
    ISSN: 2194-1831 , 1867-2493
    URL: Article
    DOI: 10.3139/105.110133
    Language: English
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2012
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  • 7
    Online Resource
    Online Resource
    Effects of Cryogenic Treatment on the Microstructure and Mechanical Properties of High-alloyed Tool Steels : Auswirkungen der Kryobehandlung auf die Mikrostruktur und die mechanischen Eigenschaften hochlegierter Werkzeugstähle
    Walter de Gruyter GmbH ; 2020
    In:  HTM Journal of Heat Treatment and Materials Vol. 75, No. 5 ( 2020-10-01), p. 73-93
    Details
    In: HTM Journal of Heat Treatment and Materials, Walter de Gruyter GmbH, Vol. 75, No. 5 ( 2020-10-01), p. 73-93
    Abstract: In this work, the influence of a cryogenic treatment on the microstructure, mechanical properties and wear resistance of the high-alloyed tool steels X38CrMoV5-3, X153CrMoV12 and ~X190CrVMo20-4 were investigated. Based on tempering curves of the steels, the heat treatment parameters were determined for the mechanical and wear specimens so that the conventionally heat-treated steels and the cryogenically treated steels featured similar hardness. The investigations showed that an almost complete transformation of retained austenite and a more homogeneous distribution of secondary carbides in the microstructure could be achieved by incorporating a cryogenic treatment. However, the cryogenic treatment does not show significantly positive effects on the investigated mechanical properties and wear resistance of the tool steels. The wear resistance of the samples was dominated by primary carbides. The cryogenic treatment would have a positive effect on large tool components with large wall thicknesses in terms of uniform and complete transformation of retained austenite throughout the entire components.
    Type of Medium: Online Resource
    ISSN: 2194-1831 , 1867-2493
    URL: Article
    DOI: 10.3139/105.110422
    Language: English
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2020
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  • 8
    Online Resource
    Online Resource
    Comparison of the Processability and Influence on the Microstructure of Different Starting Powder Blends for Laser Powder Bed Fusion of a Fe3.5Si1.5C Alloy
    MDPI AG ; 2021
    In:  Metals Vol. 11, No. 7 ( 2021-07-12), p. 1107-
    Details
    In: Metals, MDPI AG, Vol. 11, No. 7 ( 2021-07-12), p. 1107-
    Abstract: This paper examines different blends of starting materials for alloy development in the laser powder bed fusion (LPBF) process. By using blends of individual elemental, ferroalloy and carbide powders instead of a pre-alloyed gas-atomized starting powder, elaborate gas-atomization processes for the production of individual starting powders with varying alloy compositions can be omitted. In this work the model alloy Fe3.5Si1.5C is produced by LPBF from different blends of pure elemental, binary and ternary powders. Three powder blends were processed. The base material for all powder blends is a commercial gas-atomized Fe powder. In the first blend this Fe powder is admixed with SiC, in the second with the ternary raw alloy FeSiC and in the third with FeSi and FeC. After characterizing the powder properties and performing LPBF parameter studies for each powder blend, the microstructures and the mechanical properties of the LPBF-manufactured samples were analyzed. Therefore, investigations were carried out by scanning electron microscopy, wave length dispersive x-ray spectroscopy and micro hardness testing. It was shown that the admixed SiC dissolves completely during LPBF. But the obtained microstructure consisting of bainite, martensite, ferrite and retained austenite is inhomogeneous. The use of the lower melting ferroalloys FeSi and FeC as well as the ternary ferroalloy FeSiC leads to an increased chemical homogeneity after LPBF-processing. However, the particle size of the used components plays a decisive role for the dissolution behavior in LPBF.
    Type of Medium: Online Resource
    ISSN: 2075-4701
    URL: Article
    DOI: 10.3390/met11071107
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
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  • 9
    Online Resource
    Online Resource
    Influence of heat treatment on the microstructure and corrosion resistance of martensitic stainless steel
    AIP Publishing ; 2019
    In:  AIP Advances Vol. 9, No. 6 ( 2019-06-01)
    Details
    In: AIP Advances, AIP Publishing, Vol. 9, No. 6 ( 2019-06-01)
    Abstract: Heat Treatment of martensitic stainless steels is used to increase the hardness that is caused by several microstructure changes. But such a treatment does affect both mechanical properties and corrosion resistance. Existing studies about the effect of austenitizing on the material properties and the corrosion resistance show contradictory results. Here we reveal the different effects of austenitizing on the passive layer of stainless steel and thus the corrosion resistance, thermodynamic phase calculations, microstructure investigations and various electrochemical measurements are performed. By potentiodynamic polarization scans the pitting potential, the critical pitting potential and the corrosion current are determined. Impedance spectroscopy are used to gain deeper insight into the passive layer properties. The results show a strong dependency of the corrosion behavior on the heat treatment where the governing corrosion mechanism are affected differently.
    Type of Medium: Online Resource
    ISSN: 2158-3226
    URL: Article
    DOI: 10.1063/1.5094615
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2019
    detail.hit.zdb_id: 2583909-3
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  • 10
    Online Resource
    Online Resource
    Surgeon experience in glioblastoma surgery of the elderly—a multicenter, retrospective cohort study
    Springer Science and Business Media LLC ; 2023
    In:  Journal of Neuro-Oncology Vol. 161, No. 3 ( 2023-02), p. 563-572
    Details
    In: Journal of Neuro-Oncology, Springer Science and Business Media LLC, Vol. 161, No. 3 ( 2023-02), p. 563-572
    Abstract: To assess the impact of individual surgeon experience on overall survival (OS), extent of resection (EOR) and surgery-related morbidity in elderly patients with glioblastoma (GBM), we performed a retrospective case-by-case analysis. Methods GBM patients aged ≥ 65 years who underwent tumor resection at two academic centers were analyzed. The experience of each neurosurgeon was quantified in three ways: (1) total number of previously performed glioma surgeries (lifetime experience); (2) number of surgeries performed in the previous five years (medium-term experience) and (3) in the last two years (short-term experience). Surgeon experience data was correlated with survival (OS) and surrogate parameters for surgical quality (EOR, morbidity). Results 198 GBM patients (median age 73.0 years, median preoperative KPS 80, IDH-wildtype status 96.5%) were included. Median OS was 10.0 months (95% CI 8.0–12.0); median EOR was 89.4%. Surgery-related morbidity affected 19.7% patients. No correlations of lifetime surgeon experience with OS (P = .693), EOR (P = .693), and surgery-related morbidity (P = .435) were identified. Adjuvant therapy was associated with improved OS (P  〈  .001); patients with surgery-related morbidity were less likely to receive adjuvant treatment (P = .002). In multivariable testing, adjuvant therapy (P  〈  .001; HR = 0.064, 95%CI 0.028–0.144) remained the only significant predictor for improved OS. Conclusion Less experienced neurosurgeons achieve similar surgical results and outcome in elderly GBM patients within the setting of academic teaching hospitals. Adjuvant treatment and avoidance of surgery-related morbidity are crucial for generating a treatment benefit for this cohort.
    Type of Medium: Online Resource
    ISSN: 0167-594X , 1573-7373
    URL: Article
    DOI: 10.1007/s11060-023-04252-3
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2023
    detail.hit.zdb_id: 2007293-4
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